There are two kinds of SCSI cables: 50 and 68 pin cables.  The 50 pin cables are for narrow (8 bit) transfers, while 68 pin cables can support wide (16 bit) and narrow transfers.  An internal ribbon cable, whether it has 50 or 68 pins, looks a lot like a typical IDE ribbon cable, except that the SCSI cable can have a lot more nodes (connectors) on it.  Here are some shots of the two kinds of connectors.

Here's the 50 pin female connection.  From what I've seen, 50 pin internal ribbons ribbons have female connections, while the devices have the male connectors.

Here's the 68 pin male connection.  Contrary to the 50 pin ribbons, 68 pin ribbons have a male layout, while the drives are female.

These two images are of internal cables. So what happens if you find a 50 pin device in the gutter, but you only have a 68 pin cable?  If you didn't throw it out, a 68 to 50 pin converter would do the trick, provided it has the proper gender changes.  In this case the converter's 68 pin side would be female, and the 50 pin side would be female too.  Here's what it would look like.

The top end is for the 68 pin connection, while the bottom end is for the 50 pin connection.  There a many, many converters available for all different kinds of cables and devices.  

One neat type of connection that's used mainly in a server environment is called Single Connection Attachment (SCA).  It is an 80 pin plug that has 3 things in it: SCSI signals, auxiliary signals, and the power for the drive.  The reason it is used in servers is that now a drive can be easily removed/inserted into a system, with only one plug to worry about.  Here's one just for the hell of it

SCSI connector nirvana: Ram Electronics has a nice page put together with tons of different types of connectors. Some are outdated, but that doesn't mean you won't come across them.

Just for the heck of it, here's a picture of a 5-node 68 pin cable.  Note the festive yellow color; it's really given the inside of my case a nice Martha Stewart touch.

Controllers

Now that we know what the connectors look like, let's look at some SCSI controller cards.

It's a bit small but that's a picture of Adaptec's 2940 Ultra2 Wide card.  This card has two channels on it, one going at the Ultra2 Wide speed and the other going at Ultra Wide speed.  The nice thing about this type of card is that the two buses operate independently of each other.  One could have the UW bus going to pokey things like CD-ROM's and have the speedy U2W bus going to their tower of 10k RMP Seagate Cheetah's.  This particular card has 4 connectors on it, 2 for each bus. Plus, you can use all 4 plugs at once!  The picture doesn't show it well, but the 4th plug is right behind the right-hand plug; it's the black rectangle.

This isn't true of all dual channel cards, however.  For example, Adaptec's 2930U2 is a dual-channel card, but one bus has two plugs while the other only gets one.

Here's a shot of another card, an Adaptec 2940UW.  This card has only one channel, which is split up between a 68 and a 50 pin plug.  Respectively, the two plugs can handle Ultra and Ultra Wide protocols.

Drives

Just for the heck of it, I'll show you some SCSI devices.  Granted, they're just my two SCSI devices, but at least you'll see that they're not that different from IDE ones.

Well, there's the back of my hard drive, a Quantum Atlas IV, which is a 7200 RPM Ultra2 Wide LVD drive.  The connector is the usual 68 pin plug, and the jumper headers are for selecting the ID of the device.  I wish I had a picture of it, but there's a whole row of jumpers in the front of the drive that deal with things like forcing SE mode, and turning Wide mode on and off.  Note that this drive doesn't have a termination option, as it's LVD.

Here's a picture of the backs of my IDE CD-ROM and my Yamaha 44416s Ultra CD-RW.  The Yamaha is on bottom.  The back of the Yamaha has jumpers for ID select, parity, termination, and block size.  As it's an Ultra device, it only has a 50 pin connector in back.  In order to put the drive on my 68 pin cable, I had to use the above adaptor.  Losing LVD wasn't a concern because my adaptor doesn't support it anyway.  The bus still operates at 40MB/s (Ultra Wide), so I have plenty of bandwidth available.